A keypad assembly is an important component of a mobile device because it can be used to enter letters, numbers, or signs, and to produce actions or commands. A keypad assembly generally includes a main printed circuit board (PCB), a dome sheet carrying a plurality of dome switches (domes) disposed on the main PCB, and a keypad having keys on the front side and corresponding actuators on the back side. When a key is pressed, the actuator collapses the corresponding dome, which connects the circuit on the PCB and produces the intended action of the key.
There are different styles of keypads for mobile devices. One style is the so-called film-in-plastic (FIP) keypad, which is manufactured by thermo forming a polycarbonate (PC) film to the shape of the key caps and then plastic injection molding hard or relatively inflexible actuators into the back side of each key cap pocket. Slits are cut around some of the keys to make the keys more flexible and easier to be pressed down.
However, the existing design of the FIP style keypads has a number of drawbacks. First, the process of injection molding the hard actuators is not exact, which can result in gaps being present between the actuators and the domes following the assembly of the keypad into a mobile device. These gaps can make the keypad feel as if there is a loss of structural integrity during operation, as the keypad may slide in various directions while the keys are depressed. This phenomenon is referred to as keypad floating. Second, the slits cut around the keys can expose the dome sheet and the main PCB to outside dust, water or other contaminants. Third, the hard actuators can generate an abrupt and stiff tactile feedback response when they strike the corresponding domes, which can also cause a greater amount of noise to be produced during the interaction when compared to other keypads. Finally, the hard actuators, in view of their relative inflexibility, allow for a shorter key travel, which can degrade the tactile feedback quality of the keypad.